1. Field of the Invention
The present invention relates to a liquid crystal display device having flexibility and a method for manufacturing the liquid crystal display device.
2. Description of the Related Art
In recent years, technology for forming thin film transistors (TFTs) using a thin semiconductor film (with a thickness of about several tens of nanometers to several hundreds of nanometers) formed over a substrate having an insulating surface has been attracting attention. Thin film transistors are applied to a wide range of electronic devices such as ICs or electro-optical devices, and prompt development of thin film transistors that can be used as switching elements in display devices, in particular, is being pushed.
Glass substrates and quartz substrates are often used as substrates of such display devices; however, there are disadvantages to using glass substrates and quartz substrates in that they are heavy as well as breakable. In addition, increasing the size of glass substrates and quartz substrates is difficult, and glass substrates and quartz substrates are thus not suitable for mass production. For these reasons, forming display devices using flexible substrates, typically, flexible plastic films, is being attempted.
Thus, technology in which an element formation layer including thin film transistors that is formed over a glass substrate is separated from the glass substrate and transferred to another substrate, for example, to a plastic film or the like, has been proposed.
Separation and transfer techniques are proposed in References 1 and 2. In Reference 1, a separation technique in which a silicon oxide layer that is to serve as a separation layer is removed by wet etching is disclosed. In Reference 2, a separation technique in which a silicon layer that is to serve as a separation layer is removed by dry etching is disclosed.
A separation and transfer technique is also proposed in Reference 3. In Reference 3, a technique where a metal (Ti, Al, Ta, W, Mo, Cu, Cr, Nd, Fe, Ni, Co, Ru, Rh, Pd, Os, or Ir) layer is formed over a substrate, an oxide layer is formed and stacked thereover, a metal oxide layer of the metal layer is formed in the interface between the metal layer and the oxide layer, and separation from the substrate is performed during a subsequent step using this metal oxide layer is disclosed.    [Reference 1] Japanese Published Patent Application No. H8-288522    [Reference 2] Japanese Published Patent Application No. H8-250745    [Reference 3] Japanese Published Patent Application No. 2003-174153